Popular Drinking Straws Are Made Of?

I was about to throw this drinking straw, a straw from a popular fast food chain, but I noticed it was slightly bended. I remembered, it was accidentally soaked in diesel overnight.

bended red drinking strawMaybe it was a polystyrene. A petroleum-based plastic, dissolution in its own kind is normal. This articles showed that polystyrene are soluble in some oils, “Migration of Styropor to Food” and “Bad Encounters With Oil Plus Polystyrene / Styrofoam“.

I got another straw of the same type – the one which came from popular fast food chain. I also gathered two popular drinking straws, the long soft drink straw and the small and sleek juice drink straw. No tetra pack bendable straw at the moment so it was not included.

1) the red straw – from fast food chain
2) the blue straw – soft drink straw from nearby sari sari-store
3) the clear straw – juice drink in flexible pouches

I soaked all three drinking straws in diesel overnight.

The clear and red straw was slightly bended and became softer. The blue was remained straight but got softer too.

red blue and clear strawAll three were barely stretchable before soaking. The red and blue became stretchable after. The transparent became soft but not stretchable. Maybe overnight soaking was not enough.

broken and streched blue strawIn previous experiment,”Migration of Styropor to Foods”, two liquid oils partially dissolved the polystyrene polymer. No visible dissolution was observed in this.

I conducted the second test using the methods stated in, “Identifying a Plastic Container with no Recycling Symbol“.

Water test – the three prepared pellets floated in water.

Alcohol test – the three pellets floated in alcohol.

drinking straw pellents in alcoholOil test – the blue pellet sank while the other two floated.

straw pellents in oilThen the common drinking straw from sari sari-stores is made of LDPE, low density polyethylene. The red straw from  a fast food chain and the juice straw are made of polypropylene. The first contradicted the wiki statement “drinking straws are made of either polystyrene or polypropylene”.

Are you a chemical engineer working in plastic industry? Please help me regarding this matter!

The crude oil softened the straws because they came from the same origin. Or the oil might have some kind of additive that can dissolve plastic (needs verification). Popular engine oil containers are made of HDPE, the high density polyethylene. Maybe it is the polymer most inert to oil.

Marvin is the lead chocolate maker of Ben and Lyn Chocolate Inc. Has strong background in food research and development. Occasionally conducts training and lectures. Lecturer of Cocoa Foundation of the Philippines. Do coaching and consultancy services on his free time.

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